Electronic transport in porous silicon of low porosity made p+ substrate

To analyze the carriers transport in metal-porous silicon (PS) junctions, we studied the current-voltage and impedance characteristics of a series of junctions, having a typical porosity of 30% and a layer thickness ranging from 1.5 to 30 mu m. PS conductivity as a function of the annealing temperature showed two characteristic regions at 150 and 550 degrees C where the conductivity abruptly increased by several orders of magnitude. These temperatures coincide with the temperature of dissociation of Si-H-B complexes and of hydrogen effusion. After short time rinsing of high temperature annealed PS in hydrofluoric acid its resistivity returned to the initial high value it had in the as-prepared state. These results imply that hydrogen plays a key role in determining the conduction properties of PS. We argue that the hydrogen present in PS in high concentration effectively passivates the boron doping atoms. As a result the space charge region that compensates surface charges significantly widens and becomes essentially larger than the silicon wires which leads to the high resistivity of PS. Current-voltage dependencies exhibit a region of space charge limited current, which allows for the determination of the energy distribution density of states in PS. (C) 2000 Elsevier Science S.A. All rights reserved.